While the cost and performance of visual information systems are constantly improving, digital communication of visual information will have to overcome the diversity of formats used within the electronic environment of computers, display terminals, and workstations. This diversity leads to mismatches of visual data formats between different systems and devices making useful exchange of information difficult.
Integration of text, graphics and digital images in personal computers, workstations and main-frames is presently driven by the requirements of specific applications (e.g., electronic publishing, presentation graphics, computer aided circuit design). Typically, communication of graphics and pictures is minimized for lack of standards, and applications are introduced primarily as stand alone systems. For example, many systems with editors can create text and graphics page descriptions which can then be printed on a system hard copy device. The data format used for such descriptions is "native" to the system in question. Unfortunately, if the document file is transferred to a different type of system, it will likely be unintelligible (i.e., in a foreign format), even for printing, and, if usable, its presentation on a display or printer may be substantially different.
The existence of many formats is a practical necessity, since a single comprehensive format would often impose unnecessary overhead within an application. In practice, different manufactures use different native formats even for similar applications. Furthermore, new formats are continuously evolving and technological advances can reduce an accepted standard to obsolescence. As a result, it appears unlikely that ubiquitous visual communication will be grounded on the concensus use of a small group of standard formats.
Format independence, in the broadest sense, is the ability to communicate among computers, terminals and workstations when no party has knowledge of another party's format requirements. Here, the concern is with the format independent communication of visual information whose destination is a display device.
One way to achieve format independence is through pairwise conversion. In the pairwise conversion model, a conversion facility matches the format of incoming data to the format requirement of the output. Such a pairwise conversion is used in the Japanese facsimile network when dealing with conversion between group III and group IV facsimile. (See Y. Yasude et al, "Advances in Fax" PROC IEEE Vol. 73, No. 4, April 1985). The pairwise conversion approach is feasible when the number of formats is small; however, for N formats the complexity increases as N.sup.2 and the system becomes rapidly intractable.
The other approach to format independence involves use of a "universal format" to which any native format can be converted.
It is an object of the present invention to provide a system which enables format independent communication of visual data between a variety of devices. More particularly, it is an object of the invention to provide a universal format which enables format independent communication of visual data. It is a further object of the invention to provide a universal format which enables the transmission of raster display data between otherwise incompatible display devices.